E-cigarette users have greater odds of subsequent cigarette use

1. Among adolescent never smokers, electronic cigarette (e-cigarette) users had approximately 4-fold greater odds of initiating cigarette use at follow-up 2-3 years later.

2. Frequency of cigarette use was similarly patterned among both baseline e-cigarette users and non-users who initiated cigarette use at follow-up.

Evidence Rating Level: 2 (Good)

Study Rundown:E-cigarette use is rapidly growing in popularity among youth, and previous research has suggested that youth who use e-cigarettes are more likely to transition to cigarette use. Less is known about whether e-cigarettes are associated with more frequent cigarette use after initiation, or if adolescents frequently use e-cigarettes as a tool to reduce cigarette use. In this pooled, retrospective cohort study, researchers analyzed data from 3, prospective cohort studies in which high school students were surveyed on past-month cigarette and e-cigarette use in 2013-2014 and again in follow-up in 2014-2016. Compared to students who did not use e-cigarettes, a greater proportion of students who used e-cigarettes at baseline had initiated cigarette use on follow-up, and these students had approximately 4-fold higher odds for initiation of cigarette use after adjusting for sociodemographic factors. While many baseline, exclusive cigarette users had become non-smokers or exclusive, e-cigarette users at follow-up, the majority remained exclusive cigarette users or endorsed dual product use.

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These findings are limited by the length of the study, as more time may be required to observe adolescents to progress to daily smoking. Furthermore, the data may be confounded by unmeasured factors such as behavioral characteristics and peer tobacco use. Nonetheless, the study is strengthened by its large and geographically diverse sample. For physicians, these findings suggest that adolescent patients who use e-cigarettes are at greater risk for initiating cigarette use, and that appropriate interventions should be made to reduce this risk.

In-Depth [retrospective cohort]: Researchers pooled data from 3, prospective cohort studies (Southern California Children's Health Study, Happiness and Health Study, and Yale Adolescent Survey Study) to identify 6258 subjects enrolled in the ninth through twelfth grade in California or Connecticut schools. The study compared used questionnaire data that assessed sociodemographic characteristics and tobacco and alternative tobacco product use and frequency of use in the past 30 days. Baseline data was collected in 2013-2014 and follow-up data collected from the same students in 2014-2016. Experimental use was defined as initiation, but no past-30-day use of cigarettes, infrequent use was use in the 1-2 of the past 30 days, and frequent use was use in 3-5 or more of the past 30 days.

At follow-up, students with baseline e-cigarette use had greater odds for cigarette experimentation (OR = 4.57; 95%CI: 3.56-5.87), infrequent smoking (OR = 4.27; 95%CI: 2.75-6.62), and frequent smoking (OR = 3.51; 95%CI: 1.97-6.24) compared to students with no e-cigarette use. At follow-up, 9.2% of never smoking students had initiated use of cigarettes compared to 21% of e-cigarette users. Among the students who had never used cigarettes at baseline and initiated use before follow-up, similar proportions of experimentation, infrequent use, and frequent use were seen between groups at follow-up. Results did not differ by study.